Implantable prostheses are commonly used to replace or augment body tissue. In the case of breast cancer, it is sometimes necessary to remove some or all of the mammary gland and surrounding tissue that creates a void that can be filled with an implantable prosthesis. The implant serves to support surrounding tissue and to maintain the appearance of the body. The restoration of the normal appearance of the body has an extremely beneficial psychological effect on post-operative patients, eliminating much of the shock and depression that often follows extensive surgical procedures. Implantable prostheses are also used more generally for restoring the normal appearance of soft tissue in various areas of the body, such as the buttocks, chin, calf, etc.
Soft implantable prostheses typically include a relatively thin and quite flexible envelope or shell made of vulcanized (cured) silicone elastomer. The shell is filled either with a fluid such as a silicone gel or a normal saline solution. Filling of the shell takes place before or after the shell is inserted through an incision. The present invention pertains to any type of fluid-filled prosthesis, but is especially beneficial for use with gel-filled shells.
Gel-filled breast implants have been in use for over 40 years. In the 1960s, the implants were filled with a relatively thick, viscous silicone gel which created a somewhat non-responsive, unnatural feel. The implants were mostly shaped. During the 1970s and into the 1980s, a softer, more responsive silicone gel was introduced. Some implants included two lumens. Since the 1980s up to the present, improvements to the silicone gel rendered them somewhat more cohesive and firm without being non-responsive.
Confidence in silicone-gel implants ebbed at one stage, as the U.S. Food and Drug Administration had restricted the use of silicone gel-filled implants in the U.S. from 1992 through late 2006 over the concern that silicone gel leaking into the body could be harmful. Since 1992 there have been only two U.S. manufacturers of gel-filled breast implants, Inamed Corp. (now part of Allergan, Inc. of Irvine, Calif.) and Mentor Corp. (now part of Ethicon/Johnson & Johnson, New Brunswick, N.J.).
Besides safety, another important goal is maintaining breast shape after surgical implantation. During post-operative follow-up—once healing has progressed—surgeons sometimes observe undesirable alterations in the patient's breast shape, specifically signs of skin and/or soft tissue deformation, commonly known to those skilled in the art as wrinkling, knuckling or scalloping. These adverse effects usually occur at the upper or lower pole of the prostheses, along the perimeter of the prosthesis shell or at the base, i.e. the inferior portion closest to the inframammary fold, and become more evident when the recipient changes her anatomical position. Moreover, with the patient in an upright position, these unstable prostheses have been known to collapse or fold in the upper pole and knuckle in the lower pole, further increasing risk of deformed breast shape. Medical prostheses have been proposed in an attempt to eliminate these clinical problems, such as thickened perimeter areas as in U.S. Pat. No. 6,605,116 to Falcon, et al. Indeed, some current breast implant shells feature a nominal increase in wall thickness at the perimeter region, where the radius is the smallest, but adverse alterations in breast shape from folding and such continue to be seen.
Despite attempts to eliminate cosmetic flaws in implanted breast implants, there remains a need for an implant that more reliably retains a natural shape.